The present invention relates to new thermally curable one-component coating materials. The present invention also relates to a new process for preparing thermally curable one-component coating materials. The present invention additionally relates to the use of the new thermally curable one-component coating materials as clearcoat materials for producing clearcoats, especially clearcoats of multicoat color and/or effect paint systems.
Modern automobiles, especially top-class automobiles, have multicoat color and/or effect paint systems. These systems, as is known, comprise an electrocoat, a surfacer coat, antistonechip primer coat or functional coat, a color and/or effect basecoat, and a clearcoat. The multicoat paint systems are produced by means of what are termed wet-on-wet techniques, in which a clearcoat film is applied to a dried but not yet cured basecoat film and then at least basecoat film and the clearcoat film are conjointly thermally cured. This process may also include the production of the electrocoat and of the surfacer, antistonechip primer or functional coat.
The multicoat color and/or effect paint systems are known to possess the features of what has been termed automobile quality. According to European Patent EP 0 352 298 B1, page 15, line 42, to page 17, line 14 this means that the multicoat paint systems in question score highly for    (1) gloss,    (2) brightness,    (3) distinctiveness of image (DOI, i.e. of the reflected image),    (4) hiding power and uniformity thereof,    (5) dry film thickness uniformity,    (6) gasoline resistance,    (7) solvent resistance,    (8) acid resistance,    (9) hardness,    (10) abrasion resistance,    (11) scratch resistance,    (12) impact strength,    (13) intercoat and substrate adhesion, and    (14) weathering and UV stability.
Other important technological properties include    (15) high resistance to condensation,    (16) absence of any propensity toward blushing, and    (17) high stability toward tree resin and bird droppings.
The clearcoats in particular are marked by such essential technological properties as    (1) gloss,    (2) brightness,    (3) distinctiveness of image (DOI, i.e. of the reflected image),    (6) gasoline resistance,    (7) solvent resistance,    (8) acid resistance,    (9) hardness,    (10) abrasion resistance,    (11) scratch resistance,    (14) weathering and UV stability.    (15) high resistance to condensation,    (16) resistance to blushing and    (17) stability toward tree resin and bird droppings.
The quality of the clearcoats is therefore subject to particularly stringent requirements.
However, particular requirements are also imposed on the technological properties of the clearcoat materials from which these clearcoats are produced. To start with they must provide the clearcoats in the requisite quality without problems and with outstanding reproducibility. They must be preparable in a simple and outstandingly reproducible way.
Not least, they are also required to lend themselves to application on the line in the automobile plant using modern application methods, such as pneumatic spray painting with pneumatic hand sprayguns and automatic spray guns or electrostatic spray painting (ESTA) with manual spray guns or automatic high-speed rotating bells, with no problems being encountered in producing dry film thicknesses of 45 μm or more without the development of runs or pops.
For the economics of the finishing operation it is essential that the clearcoat materials on application have a high solids content. And yet the processing viscosity of the clearcoat materials must not exceed the limit determined by the finishing installation. For example, at a processing flow time of 25 seconds in accordance with DIN EN ISO 2431 (DIN ISO cup with 4 mm outlet nozzle) the clearcoat materials ought to have a solids content of >45% and in particular more than 50% by weight.
Another vital prerequisite for the applicability of the clearcoat materials by means of ESTA is that their electrical resistance is neither too high nor too low. The technical ideal is an electrical resistance in the range from 600 to 1300 kΩ.
Thermally curable one-component coating materials which comprise                hydroxyl-containing (meth)acrylate (co)polymers,        at least two crosslinking agents selected from the group consisting of tris(alkoxycarbonylamino)triazines, melamine-formaldehyde resins, and blocked polyisocyanates,        at least one additive, and        organic solventsare known.        
German Patent DE 697 029 927 T2 discloses clearcoat materials which comprise (meth)acrylate copolymers having secondary hydroxyl groups. The coating materials may also include (meth)acrylate copolymers having primary hydroxyl groups. Tris(alkoxycarbonylamino)triazines are used as obligatory crosslinking agents. As what are termed auxiliary crosslinker components it is possible, inter alia, to use blocked polyisocyanates (of which no further details are given), amino resins, and melamine resins. Their amounts, however, are not to exceed 20% by weight of the total amount of (meth)acrylate copolymers, tris(alkoxycarbonylamino)triazines, and auxiliary crosslinker components. The known clearcoat materials give clearcoats of high acid resistance, weathering stability, and yellowing stability; by way of the (meth)acrylate copolymers containing primary hydroxyl groups it is possible to adjust such key properties as scratch resistance, flexural strength, and impact strength.
International patent application WO 96/34905 A discloses clearcoat materials containing from 30 to 90% by weight, based on the solids of the clearcoat material, of a (meth)acrylate copolymer and of an alkylated melamine-formaldehyde resin or of a polyisocyanate and of a polymer having at least two isocyanate-reactive groups and also from 10 to 70% by weight, based on the solids of the clearcoat material, of a tris(alkoxycarbonylamino)triazine. The clearcoats produced from this material exhibit high abrasion resistance and etch resistance.
International Patent Application WO 97/47700 A discloses clearcoat materials comprising (meth)acrylate copolymers having secondary hydroxyl groups, tris(alkoxycarbonylamino)triazines, and, if desired, further crosslinking agents, such as amino resins and/or blocked polyisocyanates (of which no further details are given). The clearcoat materials feature high stability on storage and a low organic solvent content. Clearcoats produced from them exhibit high hardness, high gloss, good adhesion between basecoat and clearcoat, good topcoat holdout, good scratch resistance, good resistance to climatic influences, organic solvents and acids, and high resistance toward yellowing and blushing.
American patent U.S. Pat. No. 5,574,103 A or European Patent Application EP 0 604 922 A1 discloses clearcoat materials comprising hydroxyl-containing (meth)acrylate copolymers, tris(alkoxy)carbonylamino)triazines, and an arbitrary amino resin. The clearcoats produced from these materials have good etch resistance.
Known from European Patent EP 0 843 694 B1 are clearcoat materials which include at least two hydroxyl-containing (meth)acrylate copolymers, from 10 to 50% by weight, based on the solids, of a blocked polyisocyanate, and from 0 to 50% by weight, based on the solids, of a tris(alkoxycarbonylamino)triazine and/or of an arbitrary amino resin. Pyrazoles are included among many others in the blocking agents which can be used. 2,3-Dimethylpyrazole is mentioned by name. That derivative, however, is not a blocking agent, since it contains no isocyanate-reactive hydrogen atom. As the amino resin it is possible, besides many others, to use Cymel® 327, a water-soluble, reactive melamine-formaldehyde resin with a moderate to high degree of alkylation and a moderate to high imino functionality. The clearcoats produced from the clearcoat materials have a good topcoat holdout, good acid resistance, and good resistance to condensation exposure.
Last but not least, European Patent EP 1 042 402 B1 discloses clearcoat materials which comprise hydroxyl-containing (meth)acrylate copolymers and, based on the solids, from 20 to 35% by weight of an arbitrary amino resin and from 1 to 20% by weight of a tris(alkoxycarbonylamino)triazine. The total amount of the amino resins and of the tris(alkoxycarbonylamino)triazines is from 25 to 45% by weight of the solids. There is no provision for the use of blocked polyisocyanates. The clearcoats produced from the clearcoat materials exhibit high abrasion (“marring”) resistance, good etch resistance, and a good overall visual appearance.
The known clearcoat materials have the drawback that their capacity for application and their solids content on application leave much to be desired. Furthermore, the known clearcoats frequently lose their automobile quality when the clearcoat materials from which they are produced are optimized in their capacity for application and in their solids content on application.
It is therefore an object of the present invention to find new thermally curable one-component systems which no longer have the drawbacks of the prior art.
They ought to be preparable in a particularly simple way and with outstanding reproducibility and ought to be suitable for use in particular as clearcoat materials for producing clearcoats, especially clearcoats of multicoat color and/or effect paint systems.
They ought to be able to be applied on the line at the automobile plant using modern application methods, such as pneumatic spray painting with pneumatic manual spray guns and automatic spray guns or electrostatic spray painting (ESTA) using manual spray guns or automatic high-speed rotating bells, with no problems being encountered in achieving dry film thicknesses of 45 μm or more without the development of runs or pops.
On application they ought to have a high solids content, preferably >40% by weight. Despite this their processing viscosity must not exceed the limits imposed by the finishing installation. In particular the clearcoat materials at a processing flow time of 25 seconds according to DIN EN ISO 2431 (DIN ISO cup with 4 mm outlet nozzle) ought to have a solids content of >40% and in particular more than 45% by weight.
The multicoat color and/or effect paint systems produced using the novel thermally curable one-component coating materials ought to exhibit what is termed the automobile quality. In accordance with European Patent EP 0 352 298 B1, page 15, line 42, to page 17, line 14 this means that the multicoat paint systems in question ought to score highly for    (1) gloss,    (2) brightness,    (3) distinctiveness of image (DOI, i.e. of the reflected image),    (4) hiding power and uniformity thereof,    (5) dry film thickness uniformity,    (6) gasoline resistance,    (7) solvent resistance,    (8) acid resistance,    (9) hardness,    (10) abrasion resistance,    (11) scratch resistance,    (12) impact strength,    (13) intercoat and substrate adhesion, and    (14) weathering and UV stability.
Other important technological properties include    (15) high resistance to condensation,    (16) absence of any propensity toward blushing, and    (17) high stability toward tree resin and bird droppings.
The clearcoats in particular are marked by such essential technological properties as    (1) gloss,    (2) brightness,    (3) distinctiveness of image (DOI, i.e. of the reflected image),    (6) gasoline resistance,    (7) solvent resistance,    (8) acid resistance,    (9) hardness,    (10) abrasion resistance,    (11) scratch resistance,    (14) weathering and UV stability.    (15) high resistance to condensation,    (16) resistance to blushing and    (17) stability toward tree resin and bird droppings.